An MD Shares 3 Healthy Foods That Can Secretly Spike Your Blood Sugar

When it comes to the top blood-sugar-spiking foods, you likely number off processed items high in sugar and refined carbs. But wait! Did you know a class of healthy, whole foods can spike your glucose, too?

"A lot of fruits are minimal spikers, but grapes seem to be gigantic," says Means. She proposes user behavior is at play here: Grapes are often eaten on their own, without any other sources of fiber or protein. "You don't often chop up grapes and put them in yogurt—you just usually pop them in," she says. "And so I think that lack of pairing makes it more problematic."

To lower the spike, you might just need to pair your grapes with some nuts, avocado, or a wedge of cheese if you eat dairy (cheese board, anyone?). That way, the added fiber and protein can help balance the blood sugar response. 

With oatmeal, it's a similar story—only, it's what people typically add to oats that provides such a spike. Loading your oatmeal bowl with mounds of brown sugar, syrup, and chocolate chips will likely result in a large surge. "Some raw cocoa powder, almond butter, chia seeds, and some walnuts could definitely change that response," Means says. 

The type of oats you choose matters, too. According to Means, a packet of instant oatmeal (which is processed) can cause a very different blood sugar response than a cup of steel-cut or rolled oats. (If you're going to select one, dietitians note that steel-cut oats have a slightly higher fiber and protein content than rolled oats, which is good for managing blood sugar levels1.) "Those are often better for [some], but just regular, all-comer oatmeal tends to be something that spikes a lot of people."

Beans tell a trickier story. Of course, we love 'em here at mbg—they're full of fiber, protein, and important vitamins and minerals. But for some people, Means says they're a sneaky spiker. "I can eat a can of beans, which is about four servings, and have no glucose response," she says. "But there are other people who eat beans and [their glucose] spikes through the roof." 

The reason, she admits, isn't so clear, but she thinks it has something to do with the gut microbiome. She references a 2015 study in the journal 2Cell2 that put continuous glucose monitors on 800 healthy participants and gave them the same meals, assuming they would respond exactly the same. However, they found varying responses across the board—from no spikes to colossal spikes—and they discovered that their microbiome composition seemed to dictate those responses. 

It's not surprising, says Means: "The microbiome [does] a first pass on food," she says. "They're the ones who break down some of those early carbohydrates before it actually goes into the body. My co-founder David [Flinner] started eating huge amounts of chia every morning to get his fiber in, and over the course of the month after eating all this fiber day after day, he found that he no longer responded as much to beans." 

We need more research on beans in particular, but it does make sense that the microbiome would have some skin in the game. 

Focusing on high-quality whole foods is a great dietary choice for balancing blood sugar. But when it comes to specifics, some of these healthy foods can actually spike your glucose, too. "Bringing in less of the naked carbohydrate and more of the fat, protein, and fiber can often be helpful for mitigating some of this stuff," says Means. So, no, you don't necessarily have to give up grapes, oatmeal, or beans; just think about the context in which you're eating each food and tweak accordingly.